The invention relates to a screw anchor for insertion into concrete having an essentially cylindrical base body on whose outer lateral surface an external thread is provided and which has a receptacle for a fastening means arranged in the direction of the cylinder longitudinal axis originating from an axial end face, the receptacle having a load-bearing structure for the fastening means originating from the axial end face.
The invention also relates to a method for producing such a screw anchor.
To fasten components in a concrete substrate, screw anchors that are screwed into the concrete substrate are frequently used. The advantage of these screw anchors over expansion plugs or expansion impact anchors is that this type of screw anchor is also anchored securely in the concrete without an additional expansion element and a reversible fastening of the component is possible.
The screw anchor has a thread on the outside, with which the screw anchor may be screwed into a prepared borehole in the concrete substrate as well as into a receptacle running in the axial direction, in which a fastening means for fastening the component may be fixed. The receptacle features a suitable load-bearing structure for this purpose, for example, a thread for a screw.
To screw the screw anchor into the concrete substrate, a tool receptacle is required on which a tool may engage in order to rotate the screw anchor. This tool receptacle is frequently provided in or on the receptacle in order to be able to screw the screw anchor completely into the concrete substrate so that it terminates flush with the concrete surface. The disadvantage of this, however, is that the load-bearing structure of the receptacle may be damaged by the tool with the high screw-in forces that are required when screwing into a concrete substrate so that the load-bearing structure is not useable and subsequent processing of the load-bearing structure may possibly be required after the screw anchor has been mounted.
The object of the invention is making a screw anchor available, which makes it possible to screw the screw anchor into a concrete substrate simply and securely and prevent damage to the load-bearing structure in the process.
According to the invention, in the case of a screw anchor for insertion into concrete having an essentially cylindrical base body on whose outer lateral surface an external thread is provided and which has a receptacle for a fastening means arranged in the direction of the cylinder longitudinal axis originating from an axial end face, the receptacle having a load-bearing structure for the fastening means originating from the axial end face, a tool receptacle extending essentially in the direction of the cylinder longitudinal axis is provided in the receptacle, wherein the tool receptacle extends further into the receptacle than the load-bearing structure from the end face to the rotary drive of the screw anchor in the cylinder longitudinal direction.
The tool receptacle is thus configured to be long enough that the torque, which is applied via the tool to the screw anchor or to the receptacle of the screw anchor, is not transmitted completely in the area of the load-bearing structure, but at least partially outside of this area. Furthermore, due to the length of the tool receptacle, the torque is transmitted over a larger area so that strong punctual loads, which could lead to a deformation or damage of the load-bearing structure, may be reduced considerably.
The tool receptacle preferably extends over the entire axial length of the receptacle so that the load may be transmitted to the screw anchor over an area that is as large as possible. The advantage of this is that a torsion load of the screw anchor may be reduced. If the tool were to engage on the screw anchor only over a short length on the axial end face, this would produce a torsion load between a first end of the screw anchor, on which the tool engages, and the opposite second end of the screw anchor, with which the screw anchor is already inserted into the concrete borehole, at the beginning of the screw-on process due to the high screw-in forces. Because of the long tool receptacle, the load contact point is effectively distributed over the entire length of the receptacle, and also approaches nearer to the second end so that the torsion load may be reduced considerably.
In a preferred embodiment, the receptacle extends through the entire base body up to an opposing second end face. As a result, an ideal load transmission is possible because the tool may be supported on the receptacle over the entire length of the screw anchor. As a result, a twisting or a torsion of the screw anchor may be completely prevented primarily at the beginning of the screw-in process, because the load contact point is located at the same axial height with the concrete surface or with the contact surface of the screw anchor with the borehole.
In addition, the continuous receptacle makes an especially easy production of the screw anchor possible. The screw anchor may be produced, for example, from a long tube, which is already provided continuously with the tool receptacle on the inside, wherein the tube is cut to length forming several base bodies each at the desired length. The thread may be introduced before or after cutting to length. Subsequent introduction of the load bearing structure is also simplified considerably, because a cutting or milling tool may simply be slid through the entire receptacle. Cleaning the receptacle of chips is considerably simpler than with a receptacle that is closed on one side.
The object of the invention is also attained by a screw anchor for insertion into concrete having an essentially cylindrical base body on whose outer lateral surface an external thread is provided and which has a receptacle for a fastening means arranged in the direction of the cylinder longitudinal axis originating from an axial end face, the receptacle having a load-bearing structure for the fastening means originating from the axial end face, wherein the tool receptacle and the load-bearing structure extend over the entire axial length of the receptacle.
The tool receptacle is formed, for example, by at least one groove running essentially in the cylinder longitudinal axis, in which a tool may be inserted or removed from the tool receptacle in the direction of the cylinder longitudinal axis.
Several grooves running essentially parallel are preferably arranged such that the tool is centered in the middle in the receptacle and the rotational axis of the tool coincides with the cylinder longitudinal axis of the base body. As a result, a uniform load transmission of the torque on the screw anchor is possible.
The grooves form a multi-edged profile, for example, so that a conventional tool such as a screwdriver or a Torx tool may engage in the tool receptacle.
Ideally, the grooves are designed to be deeper in the radial direction than the load-bearing structure. This offers several advantages. For one, a large contact surface is provided for load transmission of the torque because of the large side surface of the grooves. The contact surface lies outside of the load-bearing structure so that the tool does not come into contact with the load-bearing structure when the screw anchor is turned and the load-bearing structure cannot be damaged when torque is applied. In addition, a simple production of the load-bearing structure is possible because of the deeper grooves. Due to the deep grooves, a corresponding cutting tool may be inserted into the receptacle and the load-bearing structure may be introduced into the receptacle by turning this cutting tool in the receptacle.
The load-bearing structure is an internal thread for example. The introduction of such a thread is considerably simpler in the case of a screw anchor according to the invention than with a conventional screw anchor. The thread is usually cut into the receptacle with a thread cutter, which is screwed into the receptacle from the axial end face. In doing so, the thread cutter may cut only one thread turn per revolution of the thread cutter, i.e., one thread section revolving by 360 degrees. Correspondingly, many revolutions of the thread cutting tool are thus required to produce a longer thread. Similarly, after completion of the thread, the thread cutting tool must be unscrewed from the thread over the entire length of the thread.
A cutting tool having several radially projecting cutting edges arranged successively in the axial direction may be used with a screw anchor according to the invention, wherein a number of cutting edges are preferably provided that corresponds to the number of desired thread turns. The tool is inserted into the receptacle, wherein the cutting edges are inserted into one of the grooves. Once the cutting tool has been inserted into the receptacle, the cutting tool is rotated around its longitudinal axis, wherein each cutting edge cuts a complete thread turn of the thread. The entire length of the thread may thus be cut with one revolution of the cutting tool. Then the cutting tool is aligned such that the cutting edges lie in a groove so that the cutting tool may be pulled out of the receptacle in the axial direction. The thread may be produced substantially quicker as a result. This is made possible in that the thread root does not project outwardly as far radially as the recess of the load receptacle. In the case of several uniformly distributed grooves, a tool having several rows of cutting edges distributed in the circumferential direction may also be used so that the cutting tool only has to be turned by the angle between two adjacent grooves to cut the entire thread length.
The receptacle of the screw anchor is preferably completely closed in the circumferential direction.
The base body may have a tubular form for example.
According to the invention, a method is also provided for producing a screw anchor according to the invention having the following steps:                providing a base body having an elongated receptacle;        introducing the tool receptacle into the receptacle; and        subsequent introduction of the load-bearing structure.        
In the case of such a method, a tube is preferably made available, in which the tool receptacle is continuously present on the inside, wherein the tube is cut to length forming several base bodies before or after introducing the load-bearing structure.
Additional advantages and features are disclosed in the following description in conjunction with the attached drawings.